The researchers noted that doesn't mean that e-cigarettes are risk-free, but it should reassure parents that teens who try the devices may simply be doing so for the novelty and aren't necessarily setting themselves up for a lifetime of nicotine addiction.

Last month, the U.S. Centers for Disease Control and Prevention warned that "vaping," or inhaling the nicotine vapors from e-cigarettes, might be a dangerous new fad that could set teens up for smoking.

In just one year, the number of kids in grades six through 12 who said they'd ever tried an e-cigarette more than doubled, rising from 3.3 percent to 6.8 percent. Among the 2.1 percent who said they were current e-cigarette users, more than three-quarters said they also smoked regular cigarettes.

Given that overlap, many health experts worried that e-cigarettes might be acting like a gateway drug, sucking kids more deeply into nicotine addiction, and law officials urged the U.S. Food and Drug Administration to regulate e-cigarettes as tobacco products.

The new study suggests that may not be the case.

Researchers surveyed 1,300 college students about their tobacco and nicotine use. The average age of study participants was 19.

"We asked what the first tobacco product they ever tried was and what their current tobacco use looked like," said researcher Theodore Wagener, an assistant professor of general and community pediatrics at the University of Oklahoma Health Sciences Center, in Oklahoma City.

Overall, 43 students said their first nicotine product was an e-cigarette. Of that group, only one person said they went on to smoke regular cigarettes. And the vast majority who started with e-cigarettes said they weren't currently using any nicotine or tobacco.

"It didn't seem as though it really proved to be a gateway to anything," said Wagener, who presented his findings at a meeting of the American Association for Cancer Research, in National Harbor, Md.

Study findings presented at medical conferences are considered preliminary since they haven't been carefully reviewed by outside experts for publication in a medical journal.